This application claims the priority of German patent document 198 03 565.9, filed Jan. 30, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a waveguide antenna which includes a waveguide section with an aperture and a shorting wall, as well as a coaxial feed and a transition from the coaxial feed to the waveguide antenna.
A hollow waveguide antenna of this type known from German patent document DE 42 13 539 A1 has a straight waveguide section with a circular cross section, one end of which is sealed by a shorting plate. The other end terminates in a horn antenna. An axially extending rod mounted on the shorting plate and two orthogonal coupling pins form a transition from a coaxial feed to a waveguide. In addition to coupling the orthogonally supplied waves, this design has the disadvantages that the feed occupies considerable space in the radial direction around the waveguide, and that a horn antenna is required for shaping the radiation pattern.
German patent document DE 40 38 817 C1 discloses a coupling device for two waveguide systems extending in superimposed planes. While this transition has proved satisfactory, this reference contains no suggestion that such a coupling device could be used in conjunction with a waveguide antenna, or how such might be accomplished.
A radiator for array antennas disclosed in from U.S. Pat. No. 3,680,138, which however is suitable only for radiating linearly polarized electromagnetic radiation. No mention is made of how a circularly polarized wave could be radiated, or how the shaping of the antenna pattern could be optimized.
The goal of the present invention is to provide a waveguide antenna with coaxial feed which can be used with both round waveguides and square waveguides, which has no parts that extend radially beyond the waveguide wall and which, despite its short axial length, has electrical power parameters that are as least as good as those of patch or slot antennas for example.
These and other objects and advantages are achieved by the waveguide antenna structure according to the invention, which includes a round or square waveguide section which is fed by two orthogonal feeds from coaxial conductors. The feeds are coupled into the waveguide section by first and second coupling devices which are arranged orthogonally about the main axis of the antenna. The waveguide section has a shorting plate at one end and an opening at the other end, and a length L=L.sub.o +1, wherein L.sub.o =1/4.lambda., .lambda. equals the operating wavelength of the antenna and 1 is less than .lambda., and 1 is the clearance between the length of the coupling devices and the length of the waveguide section.
The particular advantage of the waveguide antenna according to the invention is that it avoids the above disadvantages of conventional designs, and with a length of only slightly more than 1/4 of the operating wave length, has only a very slight coupling of the orthogonal wave components and a broadband characteristic. It also allows mounting in a tightly packed array, so that by means of simple adaptation measures, the coupling between adjacent antennas can be considerably reduced.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.